Introduction to Ultrasonic testing of Composite for Aerospace
Ultrasonic UT Testing is one of the Nondestructive testing methods to detect and measure internal flaws. UT is a good method for testing Composites for aerospace applications. Ultrasonic testing for composites uses any of the methods such as manual or automated based on the quality of work and quantity of testing.
Flaws in Aerospace Composite materials
Flaw commonly observed in aerospace composites are voids, delaminations, porosity, ply gaps, disbond or debond, foreign materials and inclusions. Composites are suitable for UT, using pulse echo from one side of the material or through transmission where there is access for both sides of composite.
Ultrasonic testing of composites usually best detects flaws perpendicular to Ultrasonic beam. Therefore, delaminations and debonds lend easy for detection. Though angle beam shear can also be suitable, straight beam UT is more widely suitable. Also, dry scan testing without using any couplant is of better choice considering the seepage of couplant into the composite that could damage the material.
UT Technique for composite Ultrasonic testing
In pulse echo through transmission technique uses straight beam longitudinal waves both for transmission and receiving on the other side. As the Aerospace composites are quite heterogeneous, the frequency selection is vital to penetrate and get desired sensitivity. Thereby, usually Ultrasonic testing of composite is performed using 500KHz and nearly up to 15MHz.
In general, back wall echo BWE method of establishing sensitivity is more prominent for aerospace composite. Though Distance gain size curves also of major use, considering the practicality BWE method is of wider use. Identification and sizing of flaws is vital to determine the acceptance of the composite. Also, there is a need to keep monitoring the loss of backwall echo throughout the scanning as loss of BWE may indicate a serious flaw.
Procedure for UT of composite material
Overlap during scanning is important to maintain the quality of testing. Usually around 15% probe overlap is sufficient during ultrasonic scanning of any composite surface. For pulse echo technique, note the amplitude and loss of back wall echo if any, once the discontinuity crosses the preset level of amplitude. And note significant loss of back wall echo in case of through transmission Ultrasonic UT testing.
Flaws larger than the probe size are measured by moving the probe and marking the centre of probe locations. 6dB drop technique method gives approximates size of the flaw. Then, evaluate the flaw acceptance as per acceptance standard.
About Aerospace NDT services at Trinity NDT Bangalore India
Trinity NDT – Aerospace NDT division provides dry scan through transmission Ultrasonic testing of aerospace composite. Each UT Level 2 inspector has ample experience in testing for aerospace applications. Learn and get your Ultrasonic testing Level 2 certification from Trinity Institute of NDT Technology.
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